It is widely accepted that hypoxia is an important factor governing the aggressiveness of tumors and that hypoxic tissue is more resistant to conventional therapeutics. Non-invasive quantitative imaging of tumor oxygenation could lead to improved clinical management and treatment of cancer patients, especially considering the recent clinical testing of angiogenesis inhibitors and oxygen-enhancing agents. Therefore, the long-term goal of this application is to develop quantitative MRI methods for the characterization of tumor oxygenation status and to evaluate its role as a potential surrogate biomarker of tumor hypoxia and treatment response. The general hypotheses for this proposal are i) MRI methods that combine the effects of contrast agents with blood oxygenation level dependent (BOLD) measurements can reliably be used to monitor tumor oxygen variations, ii) the assessment of blood volume, vascular reactivity and oxygen modulation following a maximal oxygen saturation perturbation can be used to differentiate between normoxic and hypoxic tissue and iii) contrast enhanced BOLD MRI can be used to improve treatment scheduling of anti-angiogenic agents and radiation therapy. The studies proposed focus on the development and validation of a contrast enhanced BOLD method that has the potential to separate and quantify tumor vascular reactivity and oxygen modulation. We will evaluate and incorporate corrections for the influence of local tissue pH and hematocrit on these measurements (Aim 1). The validation of the contrast enhanced BOLD parameters and tumor hypoxia will be achieved by comparison to histology and the uptake of the PET agent [18F]fluoromisonidazole (FMISO) (Aim 2). Finally, the BOLD parameters will be applied in a mouse model of cancer to plan and monitor the response of anti-angiogenic agents, oxygen-enhancing agents and radiotherapy (Aim 3). Significance: Once developed and validated these new methods will provide quantitative tools for improving clinical management and for measuring the efficacies of new anti-angiogenic and/or oxygen-enhancing treatments. It is widely accepted that low oxygenation, or hypoxia, increases the aggressiveness of tumors and decreases the effectiveness of conventional therapeutics. Imaging methods that can identify tumors with hypoxic regions and monitor changes in tumor oxygenation could lead to improved clinical management and treatment of cancer patients, especially considering the recent clinical testing of agents designed to improve tumor oxygenation. The goal of the study described in this application is to develop these imaging methods and demonstrate their clinical relevance by monitoring the response of animal cancer models to conventional treatment and promising new agents targeting hypoxic tumors. [unreadable] [unreadable] [unreadable]